Generally, valves for city water, feedwater or hot water, pipe joints, strainers, water faucet clasps, pump supplies materials, water meters, water purifiers, water feeders, hot water feeders or other such water-contact instruments are provided at halfway or end sections of pipes for city water, feedwater or hot water. These water-contact instruments are almost made of copper alloy, such as bronze or brass excellent in castability, mechanical machinability and economical efficiency. Particularly, in valves, joints, etc. made of bronze or brass, alloy added with a prescribed amount of lead is used for bronze ones in order to enhance the characteristics thereof including castability and mechanical machinability and for brass ones in order to enhance the characteristics thereof including cutting machinability and a hot-forging property. When the instruments made of bronze or brass containing lead are exposed to a fluid, such as city water, however, a lead component of the lead-containing metal deposited on the water-contact surface layer is possibly eluted into the city water.
In view of the above, the water quality standards of city water as a beverage have been prescribed by the rating identification method carried out in accordance with the specific procedure. City water has to meet the water quality standards. Since lead is a substance harmful to human bodies and the amount of lead leached has to be reduced as much as possible, restrictions on the lead leaching standard came to strengthening in April, 2003 in Japan. Under these circumstances, water-contact instruments of copper alloy produced using a so-called leadless material having lead removed from a fodder and water-contact instruments of copper alloy having the elution of lead reduced through surface treatments for a conventional lead-containing material including an acid or alkali cleaning treatment go into circulation. For example, lead elution reduction techniques are described in the following (refer, for example, to Patent Documents 1 to 3).
The lead elution prevention method described in Japanese Patent No. 3345569 (Patent Document 1) was developed by the present applicants and comprises the step of cleaning at least the water-contact surface of a piping instrument of copper alloy containing lead with a detergent comprising a nitric acid added with a hydrochloric acid as an inhibitor to form a coat the water-contact surface with the hydrochloric acid, thereby deleading the surface layer of the water-contact surface. In particular, by using benzotriazole (BTA) in place of the hydrochloric acid as an inhibitor, tarnish and corrosion are suppressed.
JP-A 2002-180267 (Patent Document 2) discloses, as a lead elution prevention technique, a lead elution prevention treatment method comprising immersing a clasp for feedwater and wastewater in a solution of any of benzotriazole-based compounds to form a film attached firmly to the surface of the clasp.
JP-A 2001-152369 (Patent Document 3) discloses, as a lead removing technique, a lead elution prevention treatment method comprising immersing a clasp for feedwater and wastewater in an etching treatment solution containing an organic carboxylic acid or a salt thereof.
In addition to the improvement in the prevention of lead elution as described above, an improvement in elution prevention of nickel adversely affecting human bodies has now been calling for urgent attention. Valves, pipe joints, water faucet clasps and other such water-contact instruments are subjected to various kinds of plating treatments, commencing with nickel-plating treatment, for the purpose of enhancing the exterior beauty, corrosion resistance and abrasion resistance. Examples of plating treatments include nickel-plating, nickel-alloy-plating, nickel-chromium-plating and nickel-tin-plating treatments. When these nickel-based plating treatments have been adopted, the coat wraps around and adheres to the spout section of a water-contact instrument.
FIG. 1 is a cross section showing a JIS wall faucet (made of CAC 406) plated with nickel-chromium alloy, and FIG. 2 is a partially enlarged cross section showing a spout section shown in FIG. 1. As shown in FIG. 2, the spout section of a water-contact instrument 1 coated with a coat 2 has a nickel coat 2b not constituting a composite layer with a chromium coat 2a. This is why the nickel coat 2b rather than the chromium coat 2a wraps around the inward portion of the spout section due to the difference in current density range between the two. In this state, when a fluid, such as city water, is supplied to the water-contact instrument 1, there is a possibility of nickel of the nickel coat 2b being eluted into the fluid.
FIG. 3 is an enlarged view showing a section “B” in FIG. 2 and, as shown, when copper (water-contact portion 1a) that is a metal having a high corrosion potential and nickel (nickel coat 2b) that is a metal having a low corrosion potential in contact with each other are water-contact with a fluid exhibiting good electrical conductivity, such as city water, to form an electrically conductive state, the nickel (nickel coat 2b) having a low corrosion potential is anode-polarized by the copper (water-contact portion 1a) having a high corrosion potential to give rise to a corrosion reaction and generate bimetallic corrosion that promotes oxidization and dissolution of nickel. Furthermore, the nickel coat 2b has a plurality of pinholes 2c and, of the pinholes, there exist those reaching the copper surface constituting the under layer of the nickel coat 2b. In consequence of a fluid exhibiting good electric conductivity, such as city water, having entered the pinholes, bimetallic corrosion is also generated there. Moreover, nickel is also eluted from the nickel coat 2b per se. The nickel elution reduction technique is disclosed in the following (refer, for example, to Patent Document 4 or 5).
The nickel elution reduction treatment method described in JP-A 2002-155391 (Patent Document 4), for example, comprises the steps of plating a water feeder made of copper or copper alloy with nickel, plating the nickel coat surface with chromium and removing the nickel coat running out the chromium coat. In the nickel-removing step, the water feeder is immersed in an oxidizing chemical, such as a sulfuric acid, for removing the nickel coat alone by dissolution. Thus, the nickel coat that has wrapped around the spout at the nickel-plating treatment can be removed by dissolution.
Japanese Patent No. 2836987 (Patent Document 5) discloses a technique for preventing the elution of nickel comprising the step of forming a thin film of aliphatic unsaturated carboxylic acid on a nickel coat plated on a ceramic substrate on which electronic parts are mounted.    Patent Document 1: Japanese Patent No. 3345569    Patent Document 2: JP-A 2002-180267    Patent Document 3: JP-A 2001-152369    Patent Document 4: JP-A 2002-155391    Patent Document 5: Japanese Patent No. 2836987